在文件~/repos/build_all/fp_octeon_56xx/build/linux/fs/rea
d_write.c中实现了read系统调用。
首先它调用宏SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)来定义一个带三个参数的系统调用。
让我们来看看这个宏：
~/repos/build_all/fp_octeon_56xx/build/linux/includ
e/linux/syscalls.h中定义了它。
#define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
#define SYSCALL_DEFINEx(x, sname, ...) \
__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
#define __SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long sys##name(__SC_DECL##x(__VA_ARGS__));
d_write.c
#define __SC_DECL1(t1, a1) t1 a1
#define __SC_DECL2(t2, a2, ...) t2 a2, __SC_DECL1(__VA_ARGS__)
#define __SC_DECL3(t3, a3, ...) t3 a3, __SC_DECL2(__VA_ARGS__)
最终SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)经过预处理后变成了
asmlinkage long sys_read (unsigned int fd, char __user *buf, size_t count);
也就是说这个函数原型声明在syscalls.h，但是定义和实现在read_write.c
上面已经分析过，系统调用中断处理是从系统调用表中查找到真正入口函数跳转过去的，sys_read自然也会在这个表中。
"~/repos/build_all/fp_octeon_56xx/build/linux/arch/mips/kernel/scall64-64.S
可以找到这个表：
.align 3
.type sys_call_table,@object
EXPORT(sys_call_table)
PTR sys_read /* 5000 */
PTR sys_write
PTR sys_open
PTR sys_close
PTR sys_newstat
PTR sys_newfstat /* 5005 */
PTR sys_newlstat
PTR sys_poll
PTR sys_lseek
PTR sys_mips_mmap
PTR sys_mprotect /* 5010 */
PTR sys_munmap
PTR sys_brk
PTR sys_rt_sigaction
PTR sys_rt_sigprocmask
PTR sys_ioctl /* 5015 */
PTR sys_pread64
PTR sys_pwrite64
PTR sys_readv
PTR sys_writev
PTR sys_access /* 5020 */
PTR sysm_pipe
PTR sys_select
PTR sys_sched_yield
PTR sys_mremap
PTR sys_msync /* 5025 */
PTR sys_mincore
PTR sys_madvise
PTR sys_shmget
PTR sys_shmat
PTR sys_shmctl /* 5030 */
PTR sys_dup
PTR sys_dup2
PTR sys_pause
PTR sys_nanosleep
PTR sys_getitimer /* 5035 */
PTR sys_setitimer
PTR sys_alarm
PTR sys_getpid
PTR sys_sendfile64
PTR sys_socket /* 5040 */
PTR sys_connect
PTR sys_accept
PTR sys_sendto
PTR sys_recvfrom
PTR sys_sendmsg /* 5045 */
PTR sys_recvmsg
PTR sys_shutdown
PTR sys_bind
PTR sys_listen
PTR sys_getsockname /* 5050 */
PTR sys_getpeername
PTR sys_socketpair
PTR sys_setsockopt
PTR sys_getsockopt
PTR sys_clone /* 5055 */
PTR sys_fork
PTR sys_execve
PTR sys_exit
PTR sys_wait4
PTR sys_kill /* 5060 */
PTR sys_newuname
PTR sys_semget
PTR sys_semop
PTR sys_semctl
PTR sys_shmdt /* 5065 */
PTR sys_msgget
PTR sys_msgsnd
PTR sys_msgrcv
PTR sys_msgctl
PTR sys_fcntl /* 5070 */
PTR sys_flock
PTR sys_fsync
PTR sys_fdatasync
PTR sys_truncate
PTR sys_ftruncate /* 5075 */
PTR sys_getdents
PTR sys_getcwd
PTR sys_chdir
PTR sys_fchdir
PTR sys_rename /* 5080 */
PTR sys_mkdir
PTR sys_rmdir
PTR sys_creat
PTR sys_link
PTR sys_unlink /* 5085 */
PTR sys_symlink
PTR sys_readlink
PTR sys_chmod
PTR sys_fchmod
PTR sys_chown /* 5090 */
PTR sys_fchown
PTR sys_lchown
PTR sys_umask
PTR sys_gettimeofday
PTR sys_getrlimit /* 5095 */
PTR sys_getrusage
PTR sys_sysinfo
PTR sys_times
PTR sys_ptrace
PTR sys_getuid /* 5100 */
PTR sys_syslog
PTR sys_getgid
PTR sys_setuid
PTR sys_setgid
PTR sys_geteuid /* 5105 */
PTR sys_getegid
PTR sys_setpgid
PTR sys_getppid
PTR sys_getpgrp
PTR sys_setsid /* 5110 */
PTR sys_setreuid
PTR sys_setregid
PTR sys_getgroups
PTR sys_setgroups
PTR sys_setresuid /* 5115 */
PTR sys_getresuid
PTR sys_setresgid
PTR sys_getresgid
PTR sys_getpgid
PTR sys_setfsuid /* 5120 */
PTR sys_setfsgid
PTR sys_getsid
PTR sys_capget
PTR sys_capset
PTR sys_rt_sigpending /* 5125 */
PTR sys_rt_sigtimedwait
PTR sys_rt_sigqueueinfo
PTR sys_rt_sigsuspend
PTR sys_sigaltstack
PTR sys_utime /* 5130 */
PTR sys_mknod
PTR sys_personality
PTR sys_ustat
PTR sys_statfs
PTR sys_fstatfs /* 5135 */
PTR sys_sysfs
PTR sys_getpriority
PTR sys_setpriority
PTR sys_sched_setparam
PTR sys_sched_getparam /* 5140 */
PTR sys_sched_setscheduler
PTR sys_sched_getscheduler
PTR sys_sched_get_priority_max
PTR sys_sched_get_priority_min
PTR sys_sched_rr_get_interval /* 5145 */
PTR sys_mlock
PTR sys_munlock
PTR sys_mlockall
PTR sys_munlockall
PTR sys_vhangup /* 5150 */
PTR sys_pivot_root
PTR sys_sysctl
PTR sys_prctl
PTR sys_adjtimex
PTR sys_setrlimit /* 5155 */
PTR sys_chroot
PTR sys_sync
PTR sys_acct
PTR sys_settimeofday
PTR sys_mount /* 5160 */
PTR sys_umount
PTR sys_swapon
PTR sys_swapoff
PTR sys_reboot
PTR sys_sethostname /* 5165 */
PTR sys_setdomainname
PTR sys_ni_syscall /* was create_module */
PTR sys_init_module
PTR sys_delete_module
PTR sys_ni_syscall /* 5170, was get_kernel_syms */
PTR sys_ni_syscall /* was query_module */
PTR sys_quotactl
PTR sys_nfsservctl
PTR sys_ni_syscall /* res. for getpmsg */
PTR sys_ni_syscall /* 5175 for putpmsg */
PTR sys_ni_syscall /* res. for afs_syscall */
PTR sys_ni_syscall /* res. for security */
PTR sys_gettid
PTR sys_readahead
PTR sys_setxattr /* 5180 */
PTR sys_lsetxattr
PTR sys_fsetxattr
PTR sys_getxattr
PTR sys_lgetxattr
PTR sys_fgetxattr /* 5185 */
PTR sys_listxattr
PTR sys_llistxattr
PTR sys_flistxattr
PTR sys_removexattr
PTR sys_lremovexattr /* 5190 */
PTR sys_fremovexattr
PTR sys_tkill
PTR sys_ni_syscall
PTR sys_futex
PTR sys_sched_setaffinity /* 5195 */
PTR sys_sched_getaffinity
PTR sys_cacheflush
PTR sys_cachectl
PTR sys_sysmips
PTR sys_io_setup /* 5200 */
PTR sys_io_destroy
PTR sys_io_getevents
PTR sys_io_submit
PTR sys_io_cancel
PTR sys_exit_group /* 5205 */
PTR sys_lookup_dcookie
PTR sys_epoll_create
PTR sys_epoll_ctl
PTR sys_epoll_wait
PTR sys_remap_file_pages /* 5210 */
PTR sys_rt_sigreturn
PTR sys_set_tid_address
PTR sys_restart_syscall
PTR sys_semtimedop
PTR sys_fadvise64_64 /* 5215 */
PTR sys_timer_create
PTR sys_timer_settime
PTR sys_timer_gettime
PTR sys_timer_getoverrun
PTR sys_timer_delete /* 5220 */
PTR sys_clock_settime
PTR sys_clock_gettime
PTR sys_clock_getres
PTR sys_clock_nanosleep
PTR sys_tgkill /* 5225 */
PTR sys_utimes
PTR sys_mbind
PTR sys_ni_syscall /* sys_get_mempolicy */
PTR sys_ni_syscall /* sys_set_mempolicy */
PTR sys_mq_open /* 5230 */
PTR sys_mq_unlink
PTR sys_mq_timedsend
PTR sys_mq_timedreceive
PTR sys_mq_notify
PTR sys_mq_getsetattr /* 5235 */
PTR sys_ni_syscall /* sys_vserver */
PTR sys_waitid
PTR sys_ni_syscall /* available, was setaltroot */
PTR sys_add_key
PTR sys_request_key /* 5240 */
PTR sys_keyctl
PTR sys_set_thread_area
PTR sys_inotify_init
PTR sys_inotify_add_watch
PTR sys_inotify_rm_watch /* 5245 */
PTR sys_migrate_pages
PTR sys_openat
PTR sys_mkdirat
PTR sys_mknodat
PTR sys_fchownat /* 5250 */
PTR sys_futimesat
PTR sys_newfstatat
PTR sys_unlinkat
PTR sys_renameat
PTR sys_linkat /* 5255 */
PTR sys_symlinkat
PTR sys_readlinkat
PTR sys_fchmodat
PTR sys_faccessat
PTR sys_pselect6 /* 5260 */
PTR sys_ppoll
PTR sys_unshare
PTR sys_splice
PTR sys_sync_file_range
PTR sys_tee /* 5265 */
PTR sys_vmsplice
PTR sys_move_pages
PTR sys_set_robust_list
PTR sys_get_robust_list
PTR sys_kexec_load /* 5270 */
PTR sys_getcpu
PTR sys_epoll_pwait
PTR sys_ioprio_set
PTR sys_ioprio_get
PTR sys_utimensat /* 5275 */
PTR sys_signalfd
PTR sys_ni_syscall
PTR sys_eventfd
PTR sys_fallocate
PTR sys_timerfd_create /* 5280 */
PTR sys_timerfd_gettime
PTR sys_timerfd_settime
PTR sys_signalfd4
PTR sys_eventfd2
PTR sys_epoll_create1 /* 5285 */
PTR sys_dup3
PTR sys_pipe2
PTR sys_inotify_init1
PTR sys_preadv
PTR sys_pwritev /* 5390 */
PTR sys_rt_tgsigqueueinfo
PTR sys_perf_event_open
PTR sys_accept4
PTR sys_recvmmsg
.size sys_call_table,.-sys_call_table
最后要提供给应用程序使用read这个系统调用，所以在unistd.h里提供了系统调用号和系统调用的原型。
#define __NR_read 64
__SYSCALL(__NR_read, sys_read)